When looking at the error-logging of Apex, there are a massive amount of the same errors.

The package ‘www_flow.accept’ is a genuine Apex-package, so it doesn’t look like an application thing. After poking around on Metalink and forums, the following was found:

Metalink: this could be the result of database bug 5228292 or 4752541 (fixed in 10.2.0.3 introducing bug 5705795, also fixed in 10.2.0.3, also one-off patch available) and the problem went away after issuing ALTER SYSTEM FLUSH SHARED_POOL as SYS. So yes, this is a workaround, and yes I put this in a job every night. Did it help? Unfortunately not.

In the forums it seems that not using ‘clearing caches’ in the sessions is causing some trouble, and one of the solutions (sorry, could not find the URL and the author anymore) we used, and I quote the author:

I had the exact same problem when I tried to submit my login credintials. I got around it by adding a process to my login page.

Process type: Clear Cache For Current Session (removes all state for current session)
Process point: On Load – Before header.

After I start using this process I haven’t seen the error.

Implemented this (by our developer), and … now we wait. Don’t know of it helped yet, but it looks like an old story: not neatly programming will be punished, also by Apex. Whether it helped or not with me, maybe it helps you to solve your problem or gives you a clue.